Conventionally, a solid electrolytic capacitor of a structure shown in FIG. 6 is known. This solid electrolytic capacitor includes a capacitor element 6 including an anode element 3 including a sintered body of a valve-action metal (tantalum, niobium, titanium, aluminum, etc.), a dielectric coating layer 4 formed on a surface of the anode element 3 by oxidizing the surface, and a cathode layer 5 in which a solid electrolyte layer 5a made of a conductive inorganic material such as manganese dioxide or conductive organic material such as TCNQ complex salt and a conductive polymer and a cathode lead layer 5b made of carbon, silver, etc. are sequentially formed. An anode lead frame 11 is connected to an anode lead member 7 planted on one end surface of the anode element 3 while a cathode lead frame 12 is connected to the cathode layer 5. An enclosure resin 8 made of epoxy resin etc. coats the capacitor element 6 to seal the capacitor. The anode lead frame 11 and the cathode lead frame 12 are bent along the enclosure resin 8 (see JP 10-64761 A).
In the solid electrolytic capacitor of the above-described structure, because both an upper face and a lower face of the capacitor element need be coated with the enclosure resin, there is a problem that a size of the capacitor element cannot be sufficiently large relative to an overall size as a solid electrolytic capacitor finished product.
Accordingly, as shown in FIG. 7, the present applicant has proposed a technique in which a capacitor element 6 is mounted on a platy anode terminal 1 and a cathode terminal 2 to make a gap between the capacitor element 6 and an outer periphery of an enclosure resin 8 as small as possible, so that the capacitor element 6 with a large occupied volume relative to an overall size of a solid electrolytic capacitor finished product can be incorporated (JP 2001-244145 A).
In this solid electrolytic capacitor, because the lead terminal is in direct contact with a circuit board etc., a lead frame need not be bent along the enclosure resin as conventionally, so that a current path from the capacitor element to the circuit board can be shortened to reduce an ESR and ESL in the solid electrolytic capacitor finished product.
Furthermore, as shown in FIG. 8, a distance between current paths of each of an anode and a cathode to an external circuit board can be shortened by extending the cathode terminal 2 of the solid electrolytic capacitor to a vicinity of the anode terminal 1, so that an ESL in a high-frequency area can be further reduced.
When the above-described solid electrolytic capacitor proposed by the present applicant is connected to a circuit board etc., as shown in FIG. 9(a), a solder 50 is pasted on a land 40 formed on the circuit board 30, and then the solid electrolytic capacitor is mounted thereon.
However, in the solid electrolytic capacitor, a difference in area between an anode exposed portion of the anode terminal 1 exposed from the enclosure resin 8 and a cathode exposed portion of the cathode terminal 2 exposed from the enclosure resin 8 is greater than that in the conventional capacitor. Therefore, there is a problem that as shown in FIG. 9(b), the solder 50 pasted on the land 40 with a larger area corresponding to the cathode exposed portion shrinks by surface tension and pushes up the solid electrolytic capacitor mounted on the solder 50 to cause displacement, resulting in a defective appearance and disconnection in the anode terminal.
The present invention provides, in view of the above-described problem, a solid electrolytic capacitor capable of being soldered well to a circuit board etc. while maintaining an ESL reduction effect previously proposed by the present applicant.